arXiv subjects
Publications and source records attributed to C. Papovich.
We use the source counts measured with the Multiband Imaging Photometer for Spitzer (MIPS) at 24, 70, and 160 microns to determine the 5-sigma confusion limits due to extragalactic sources: 56 micro-Jy, 3.2 and 40 mJy at 24, 70 and 160 microns, respectively. We also make predictions for confusion limits for a number of proposed far infrared missions of larger aperture (3.5 to 10m diameter).
We present sub-millimeter statistical detections of galaxies discovered in the 5'x5' Spitzer Early Release Observations (to 4-15 microJy 5 sigma at 3.6-8 microns, 170 microJy at 24 microns) through a stacking analysis of our reanalysed SCUBA 8mJy survey maps, and a Spitzer identification of a new sub-millimeter point source in the 8mJy survey region. For sources detected at 5.8 or 8 microns (154 and 111 sources respectively), we detect positive skews in the sub-millimeter flux distributions at 99.2-99.8% confidence using Kolmogorov-Smirnov tests, at both 850 microns and 450 microns. We also marginally detect the Spitzer 24 micron galaxies at 850 microns at 97% confidence, and place limits on the mean sub-millimeter fluxes of the 3.6 and 4.5 micron sources. Integrating the sub-millimeter fluxes of the Spitzer populations, we find the 5.8 micron galaxies contribute 0.12 +/- 0.05 nW/m^2/sr to the 850 micron background, and 2.4 +/- 0.7 nW/m^2/sr to the 450 micron background; similar contributions are made by the 8 micron-selected sample. We infer that the populations dominating the 5.8 and 8 micron extragalactic background light also contribute around a quarter of the 850 micron background and the majority of the 450 micron background.
We investigate Extremely Red Objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 micron) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the IRAC camera allows us to detect 64 EROs in only 12 minutes of IRAC exposure time, by means of an R-[3.6] color cut (analogous to the traditional red R-K cut). A pure infrared K-[3.6] red cut detects a somewhat different population and may be more effective at selecting z > 1.3 EROs. We find 17% of all galaxies detected by IRAC at 3.6 or 4.5 micron to be EROs. These percentages rise to about 40% at 5.8 micron, and about 60% at 8.0 micron. We utilize the spectral bump at 1.6 micron to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 micron). We conclude that two-thirds of all EROs lie at redshift z > 1.3. Detections at 24 micron imply that at least 11% of 0.6 < z < 1.3 EROs and at least 22% of z > 1.3 EROs are dusty star-forming galaxies.
We have measured the rest--frame lambda~1500 Ang comoving specific luminosity density of star--forming galaxies at redshift 3.5<z<6.5 from deep images taken with the Hubble Space Telescope (HST)and the Advanced Camera for Surveys (ACS), obtained as part of the Great Observatories Origins Deep Survey (GOODS). We used color selection criteria to construct samples of star--forming galaxies at redshifts z~4, 5 and 6, identified by the signature of the 912 Ang Lyman continuum discontinuity and Lyman-alpha forest blanketing in their rest--frame UV colors (Lyman--break galaxies). The ACS samples cover ~0.09 square degree, and are also relatively deep, reaching between 0.2 and 0.5 L_3^*, depending on the redshift, where $L_3^*$ is the characteristic UV luminosity of Lyman--break galaxies at z~3. The specific luminosity density of Lyman--break galaxies appears to be nearly constant with redshift from z~3 to z~6, although the measure at z~6 remains relatively uncertain, because it depends on the accurate estimate of the faint counts of the z~6 sample. If Lyman--break galaxies are fair tracers of the cosmic star formation activity, our results suggest that at z~6 the universe was already producing stars as vigorously as it did near its maximum several Gyr later, at 1<~z<~3. Thus, the onset of large--scale star formation in the universe is to be sought at around z~6 or higher, namely at less than ~7% of the current cosmic age.
We report early results on galaxies at z~6, selected from Hubble Space Telescope imaging for the Great Observatories Origins Deep Survey. Spectroscopy of one object with the Advanced Camera for Surveys grism and from the Keck and VLT observatories a shows a strong continuum break and asymmetric line emission, identified as Lya at z=5.83. We detect only five spatially extended, z~6 candidates with signal-to-noise ratios > 10, two of which have spectroscopic confirmation. This is many fewer than would be expected if galaxies at z=6 had the same luminosity function as those at z=3. There are many fainter candidates, but we expect substantial contamination from foreground interlopers and spurious detections. Our best estimates favor a z=6 galaxy population with fainter luminosities, higher space density, and similar co-moving ultraviolet emissivity to that at z=3, but this depends critically on counts at fluxes fainter than those reliably probed by the current data.
We present a multi-wavelength study of RX J0848+4456, a cluster of galaxies discovered through X-ray emission in the ROSAT Deep Cluster Survey. Our observations consist of WFPC2 imaging, optical spectra, and X-ray data collected with the Chandra observatory. We find that RX J0848+4456 consists of an X-ray emitting cluster of galaxies at a redshift of z=0.570 and a group at slightly lower redshift, z=0.543, with little X-ray emission. This lower redshift system, however, is a gravitational lens, with the lensed galaxy an unusual AGN or star-forming system at z=3.356. The cluster has an X-ray temperature of kT = 3.6 +/- 0.4 keV, a bolometric luminosity of 1.0e44 +/- 0.3e44 erg/s and a velocity dispersion of 670 +/- 50 km/s. These values all agree with the low redshift correlations for clusters of galaxies, implying a relaxed system with the ICM in equilibrium with the dark matter potential. The lower redshift group of galaxies at z=0.543 has, at most 1/5, more likely 1/10, of the X-ray luminosity of RX J0848+4456. Despite being a gravitational lens, this is a low mass system, with an X-ray temperature of kT = 2.3 +0.5 -0.4 keV and a velocity dispersion of only 430 +/- 20 km/s. Our observations show the importance of detailed studies of clusters of galaxies when using them as probes of cosmological mass functions.